1. Field of the Invention
The present invention relates to a piezoelectric device that may be utilized as, for instance, a filter, a resonator or a vibrator, and a method of manufacturing this piezoelectric device.
2. Discussion of the Background
A sealed vibration space must be formed around a first electrode and a second electrode in this type of piezoelectric device. The degree of airtightness in such a vibration space and its volumetric capacity directly affect the characteristics of the piezoelectric device. Thus, when forming a vibration space, it is crucial to ensure that the vibration space achieves a high degree of airtightness, that it is supported by a film structure that does not cause any reduction in the degree of airtightness and that it maintains a constant spatial volume. In addition, it is also essential to ensure that no residue from the manufacturing process remains, in order to prevent the occurrence of characteristics defects.
The publications in the known art disclosing technologies for vibration space formation include Japanese Unexamined Patent Publication No. 41309/1989 and Japanese Unexamined Patent Publication No. 167381/1993. Japanese Unexamined Patent Publication No. 41309/1989 discloses that after applying a resist resin to a vibration portion of a piezoelectric element, a cover resin (a hollow layer) is applied onto a surface of the piezoelectric element while securing an opening communicating with a portion of an end edge of the resist resin. Next, after the cover resin is dried, the resist resin is dissolved by using an organic solvent or the like and is further discharged to the outside through the opening in the cover resin. In addition, the cavity formed by removing the resist resin is washed by means such as ultrasonic cleaning. Then, the opening is sealed to form a sealed vibration space.
Japanese Unexamined Patent Publication No. 167381/1993 discloses that after applying a resist resin to a vibration portion of a piezoelectric element, a resin layer (hollow layer) having an opening ranging over an area smaller than the planar area of the resist resin layer is formed on the resist resin. Then, after the resin layer (hollow layer) is dried, the resist resin is dissolved and discharged to the outside through the opening in the cover resin. By sealing the opening with a sealing layer, a sealed vibration space is formed. The sealing layer includes a first sealing layer and a second sealing layer. The first sealing layer has an indented portion to enclose the cavity area and is pasted onto the hollow layer. The second sealing layer is pasted onto the first sealing layer to seal the indented portion of the first sealing layer and the opening continuous with the cavity.
However, the prior art technologies described above do not readily satisfy the requirement of the vibration space discussed earlier. For instance, in the invention disclosed in Japanese Unexamined Patent Publication 41309/1989, the opening provided to facilitate the removal of the resist resin and to wash out the resist resin is located at the end edge of the hollow layer and residue of the resist resin tends to remain inside the cavity. In addition, since the thickness of the hollow layer around the opening is extremely small, cracks and the like occurring in this area may reduce the degree of airtightness.
In the invention disclosed in Japanese Unexamined Patent Publication No. 16738 1/1993, the airtightness cannot be sustained if a misalignment which occurs between the opening continuous with the cavity and the indented portion of the first sealing layer or between the cavity and the indented portion at the first sealing layer.
It is an object of the present invention to provide a piezoelectric device having a vibration space that achieves a high degree of airtightness, and a manufacturing method thereof.
It is a further object of the present invention to provide a piezoelectric device having a vibration space of which the airtightness is not readily reduced, and a manufacturing method thereof.
It is a still further object of the present invention to provide a piezoelectric device having a vibration space that maintains a constant spatial volume, and a manufacturing method thereof.
It is a still further object of the present invention to provide a piezoelectric device achieving a structure that does not readily allow residue from the manufacturing process to remain in the vibration space, and a manufacturing method thereof.
In order to achieve the objects described above, the present invention discloses a piezoelectric device realized in two modes.
The piezoelectric device in the first mode comprises a piezoelectric element, a first film structure and a second film structure. The piezoelectric element includes a piezoelectric substrate, at least one first electrode and at least one second electrode. The first electrode is provided at a first surface of the piezoelectric substrate, whereas the second electrode is provided at a second surface of the piezoelectric substrate which faces opposite the first electrode.
The first film structure includes a first hollow layer and a first sealing layer. The first hollow layer has a first surface, an opposing second surface and at least one first cavity. The first cavity has a uniform width and extends between the first and second surfaces of the first hollow layer around a vibration portion of the piezoelectric element where the first electrode is provided. The first surface of the first hollow layer is disposed on the first surface of the piezoelectric substrate, and the first sealing layer is disposed on the second surface of the first hollow layer to seal the first cavity.
The second film structure includes a second hollow layer and a second sealing layer. The second hollow layer has a first surface, an opposing second surface and at least one second cavity. The second cavity has a uniform width and extends between the first and second surfaces of the second hollow layer around a vibration portion of the piezoelectric element where the second electrode is provided. The first surface of the second hollow layer is disposed on the second surface of the piezoelectric substrate, and the second sealing layer is disposed on the second surface of the second hollow layer to seal the second cavity.
As described above, in the piezoelectric device according to the present invention, the first electrode is provided at the first surface of the piezoelectric substrate. The second electrode, located at the second surface of the piezoelectric substrate, faces opposite the first electrode. The first and second electrodes constitute a vibration portion. As a result, piezoelectric vibration characteristics determined by the first and second electrodes are achieved.
The first hollow layer forms the first cavity around the vibration portion where the first electrode is provided. The first sealing layer is disposed on the first hollow layer to seal the first cavity. The second hollow layer forms the second cavity around the vibration portion where the second electrode is provided. The second sealing layer is disposed on the second hollow layer to seal the second cavity. Consequently, piezoelectric vibration occurs in the first and second cavities sealed by the first and second film structures respectively.
Since the first cavity has a uniform width and extends between the first and second surfaces of the first hollow layer, the resist resin, which is utilized under normal circumstances to form the first cavity, can be completely removed. Thus, characteristics defects caused by the presence of residual resist resin can be prevented.
The first sealing layer is disposed on the second surface of the first hollow layer to seal the first cavity. Since such a first sealing layer only needs to be disposed on the plane of the first hollow layer, the alignment of the first sealing layer relative to the first hollow layer, which is essential in the prior art, does not need to be performed. Thus, there is no likelihood of an erroneous alignment, which would reduce the degree of airtightness.
In addition, since the first sealing layer only needs to be disposed on the plane of the first hollow layer, a vibration space achieving a high degree of airtightness is formed. Furthermore, since a sufficient overlapping area is assured by positioning the first sealing layer on the plane of the first hollow layer, a vibration space, the airtightness of which is less readily reduced, is achieved.
The volumetric capacity of the first cavity (vibration space) is set at a constant spatial volume determined by the planar area of the first cavity and the layer thickness of the first hollow layer. Thus, constant characteristics can be assured.
It is obvious that the advantages achieved in the first film structure described above are also realized in the second film structure.
The method of manufacturing the piezoelectric device in the first mode described above includes a process for forming the first film structure and a process for forming the second film structure.
The process for forming the first film structure includes a step in which a first resist resin is applied to a first surface of a piezoelectric substrate having numerous sets of electrodes each constituted of a first electrode and a second electrode facing opposite each other at the first and second surface, so as to individually cover the first electrodes, a step in which a first resin layer used for the formation of a first hollow layer is formed at the first surface of the piezoelectric substrate over the area around the first resist resin, a step in which the first resist resin is removed and a through hole is formed for each first electrode and a step in which a first sealing layer is formed over the first resin layer.
The process for forming the second film structure includes a step in which a second resist resin is applied to the second surface of the piezoelectric substrate so as to individually cover the second electrodes, a step in which a second resin layer used for the formation of a second hollow layer is formed at the second surface of the piezoelectric substrate over the area around the second resist resin, a step in which the second resist resin is removed and a through hole is formed for each second electrode and a step in which a second sealing layer is formed over the second resin layer.
When these processes are implemented, hardly any residue from the manufacturing process remains in the first and second cavities (vibration spaces). In addition, a piezoelectric device which has vibration spaces that achieve a high degree of airtightness which is not readily reduced, and which achieves a constant spatial volume, can be manufactured.
The piezoelectric device in the second mode comprises a piezoelectric element, a first film structure, a second film structure and a third film structure. The piezoelectric element includes a piezoelectric substrate, at least one first electrode and at least one second electrode.
The at least one first electrode is provided at a first surface of the piezoelectric substrate and the at least one second electrode is provided at an opposing second surface of the piezoelectric substrate so that the at least one first electrode and the at least one second electrode are opposite each other. The at least one first electrode and the at least one second electrode constitute a vibration portion at the piezoelectric element.
The first film structure includes a plurality of first split layers and a first sealing layer. The plurality of first split layers each have a first surface and an opposing second surface and are positioned over at least one gap. At least one first cavity is formed by the at least one gap at the vibration portion of the piezoelectric element which includes the first electrode. The first surface of the plurality of first split layers is disposed on the first surface of the piezoelectric substrate, and the first sealing layer is disposed on the second surface of the plurality of first split layers to seal the at least one first cavity.
The second film structure includes a plurality of second split layers and a second sealing layer. The plurality of second split layers each have a first surface and an opposing second surface and are positioned over at least one gap. At least one second cavity is formed by the at least one gap at the vibration portion of the piezoelectric element which includes the second electrode. The first surface of the plurality of second split layers is disposed on the second surface of the piezoelectric substrate, and the second sealing layer is disposed on the second surface of the plurality of second split layers to seal the at least one second cavity.
The third film structure includes a third sealing layer and a fourth sealing layer which are each disposed on one of two opposing side surfaces of an assembly that includes the piezoelectric element, the first film structure and the second film structure to seal the at least one first cavity and the at least one second cavity at the two side surfaces.
In the piezoelectric device in the second mode, the first electrode is provided at the first surface of the piezoelectric substrate. The second electrode, located at the second surface of the piezoelectric substrate, faces opposite the first electrode. As a result, piezoelectric vibration characteristics determined by the first and second electrodes are achieved.
The first hollow layer forms the first cavity around the vibration portion where the first electrode is provided. The first sealing layer is formed over the first hollow layer. The second hollow layer forms the second cavity around the vibration portion where the second electrode is provided. The second sealing layer is formed over the second hollow layer. The third and fourth sealing layers of the third film structure are each formed at one of the two side surfaces of the assembly which includes the piezoelectric element, the first film structure and the second film structure to seal the first and second cavities at the two side surfaces. Thus, the piezoelectric element engages in piezoelectric vibration inside the first and second cavities sealed by the first film structure, the second film structure and the third film structure.
Since the two first split layers constituting the first film structure are provided over a distance from each other at the first surface of the piezoelectric substrate creating the first cavity corresponding to the distance between them at the first electrode, it is not necessary to use a resist resin, which is normally required to form the first cavity. Thus, characteristics defects caused by residual resist resin can be prevented.
The first sealing layer is disposed on the second surface of the first split layers to seal the first cavity created by the gap formed between the first split layers. Since the first sealing layer only needs to be disposed on the plane of the first split layers, alignment of the first sealing layer relative to the first split layers is not necessary, which is essential in the prior art. Thus, there is no risk of the airtightness becoming reduced as a result of an erroneous alignment.
In addition, since the first sealing layer only needs to be disposed on the plane of the first split layers, a vibration space achieving a high degree of airtightness is formed. Furthermore, since a sufficient overlapping area is assured by positioning the first sealing layer on the plane of the first split layers, a vibration space, the airtightness of which is less readily reduced, is achieved.
The volumetric capacity of the first cavity (vibration space) is set at a constant spatial volume determined by the planar area of the gap ranging over the distance between the first split layers and the layer thickness of the first split layers. Thus, constant characteristics can be assured.
Since the second split layers are provided over a distance from each other at the second surface of the piezoelectric substrate creating the second cavity corresponding to the distance between them at the second electrode, it is not necessary to use a resist resin, which is normally required to form the second cavity. Thus, characteristics defects caused by residual resist resin can be prevented.
The second sealing layer is disposed on the second surface of the second split layers to seal the second cavity created by the gap formed between the second split layers. Since the second sealing layer only needs to be disposed on the plane of the second split layers, alignment of the second sealing layer relative to the second split layers in not necessary, which is essential in the prior art. Thus, there is no risk of the airtightness becoming reduced as a result of an erroneous alignment.
In addition, since the second sealing layer only needs to be disposed on the plane of the second split layers, a vibration space achieving a high degree of airtightness is formed. Furthermore, since a sufficient overlapping area is assured by positioning the second sealing layer on the plane of the second split layers, a vibration space, the airtightness of which is less readily reduced, is achieved.
The volumetric capacity of the second cavity (vibration space) is set at a constant spatial volume determined by the planar area of the gap ranging over the distance between the second split layers and the layer thickness of the second split layers. Thus, constant characteristics can be assured.
The first cavity formed by the first film structure and the second cavity formed by the second film structure are sealed by the third film structure. Since the third film structure is formed at the two side surfaces of the assembly which includes the piezoelectric element, the first film structure and the second film structure, a sufficient bonding area or a sufficient pasting area is assured for the third film structure to achieve vibration spaces, the airtightness of which is less likely to become reduced.
In addition, since the third film structure is formed at the two side surfaces, the volumetric capacities of the first and second cavities do not fluctuate. The volumetric capacities of the first and second cavities are each set at a constant spatial volume determined by the planar area of the gap corresponding to the distance between the second split layers and the layer thickness of the second split layers. Thus, constant characteristics can be assured.
The method of manufacturing the piezoelectric device in the second mode described above includes a process for forming the first film structure and a process for forming the second film structure.
The process for forming the first film structure includes a step in which a first resist resin is applied in strips at a first surface of a piezoelectric substrate having numerous sets of electrodes each constituted of a first electrode and a second electrode facing opposite each other at the first and second surface so as to commonly cover a plurality of first electrodes, a step in which a first resin layer used to form a first hollow layer is formed at the first surface of the piezoelectric substrate in the area around the first resist resin, a step in which the first resist resin is removed and a through hole that contains the plurality of first electrodes is formed and a step in which a first sealing layer is formed over the first resin layer.
The process for forming the second film structure includes a step in which a second resist resin is applied in strips to the second surface of the piezoelectric substrate so as to commonly cover a plurality of second electrodes, a step in which a second resin layer used for the formation of a second hollow layer is formed at the second surface of the piezoelectric substrate in the area around the second resist resin, a step in which the second resist resin is removed and a through hole that contains the plurality of second electrodes is formed and a step in which the second sealing layer is formed over the second resin layer.
When these processes are implemented, hardly any residue from the manufacturing process remains in the first and second cavities (vibration spaces). In addition, a piezoelectric device which has vibration spaces that achieve a high degree of airtightness which is not readily reduced, and which achieves a constant spatial volume, can be manufactured.
The present invention also discloses specific examples of application in a piezoelectric device that may be used as, for instance, a filter, a resonator, a vibrator or the like.